SIP/H.323 zones 45
Off-net dialing plan
When dialing to the PSTN, the Call Server determines that the call
destination is off-net by analyzing the digits that must be preconfigured at
major Call Servers in the network.
If routed over a Virtual Trunk,a request is sent to the NRS to determine
the location of public E.164 numbers. The NRS is configured with a list
of potential alternate routes that can be used to reach a certain dialed
number. Each route is configured with a unique route cost to determine
the least-cost route.
The NRS replies with the address information for E.164 numbers. It also
provides a list of alternative SIP or H.323 endpoints, sorted by cost. If a
terminating endpoint resource is busy when a call attempt is made, the
originating endpoint tries the next alternative. If no alternative is available
over the IP network, the originating endpoint steps to the nextentr y on its
route list, which could be a TIE or PSTN alternate route.
Routing calls

SRG user call to an SRG PSTN

The SRG user telephone is registered at the main office. The SRG user
telephones are physically located at the branch office,so routing of local
PSTN calls back to the branch office is essential, even if they are registered
with the main office.
Branch office behavior of the SRG user telephones at the main office is
configured by setting branch office zone characteristics through LD 117 at
the main office.

SRG PSTN to an SRG telephone (DID call)

If the DN is valid and can terminate, call termination at the branch office is
treated differently for IP Phones and non-IP Phones, as follows:
•IP Phones—If the telephone is registered to the SRG (Local Mode),
the call is terminated locally. If the telephone is not registered to the
SRG (Normal Mode), the call is routed through a Virtual Trunkto the
main office.
•Non-IP Phones—Calls are terminated locally (within the branch office).
SIP/H.323 zones
In a SIP/H.323 network, each NRS controls one SIP/H.323 zone. Each
zone can consist of many SIP/H.323 endpoints. If a call terminates beyond
the call originator zone, the SIP Redirect Server or H.323 Gatekeeper of the
called party zone provides the endpoint information to set up the connection.
Nortel Communication Server 1000
Main Office Configuration Guide forSRG 50
NN43001-307 02.02 Standard
Release 5.0 3 December 2007
Copyright© 2005-2007, Nor tel Networks
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